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In just 12 days, the world gets half of its annual rainfall

Some days are dry, and others are wet. And some are really wet. A new study reveals that any particular place on the globe gets half its annual rainfall—on average—in just 12 days.

For their analysis, the researchers looked at daily rainfall data gathered at 185 sites worldwide from 1999 through 2014. That 16-year period was long enough to capture year-to-year variations in rainfall caused by El Niño and other short-term climate cycles. They also focused on weather stations located within 50° of the equator, which allowed them to use satellite data both to validate their data and to extrapolate their findings to broader regions.

On average, the wettest day at each site received a full month’s worth of rain. Also, half of a site’s annual precipitation falls over the course of just 12 days, the researchers report this month in Geophysical Research Letters. Which specific days are the wettest varies from place to place and season to season, of course, but the pattern holds worldwide.

The researchers also used 36 different climate models to assess how rainfall trends might change in the future. In particular, they looked at estimates for daily rainfall for the years 2085 through 2100 for a scenario in which the atmospheric concentration of planet-warming carbon dioxide (CO2) rises to 936 parts per million (ppm) in the year 2100. (Today, CO2 levels are about 408 ppm.) In that warmer world, the air can hold more water vapor, and thus extreme rainfall will become even more extreme. In the last 16 years of this century, any particular locale can expect half a year’s rainfall to occur in just 11 days. Get those umbrellas while you can.